NAME
Unix::Passwd::File - Manipulate /etc/{passwd,shadow,group,gshadow}
entries
VERSION
This document describes version 0.250 of Unix::Passwd::File (from Perl
distribution Unix-Passwd-File), released on 2017-11-06.
SYNOPSIS
use Unix::Passwd::File;
# list users. by default uses files in /etc (/etc/passwd, /etc/shadow, et al)
my $res = list_users(); # [200, "OK", ["root", ...]]
# change location of files, return details
$res = list_users(etc_dir=>"/some/path", detail=>1);
# [200, "OK", [{user=>"root", uid=>0, ...}, ...]]
# also return detail, but return array entries instead of hash
$res = list_users(detail=>1, with_field_names=>0);
# [200, "OK", [["root", "x", 0, ...], ...]]
# get user/group information
$res = get_group(user=>"paijo"); # [200, "OK", {user=>"paijo", uid=>501, ...}]
$res = get_user(user=>"titin"); # [404, "Not found"]
# check whether user/group exists
say user_exists(user=>"paijo"); # 1
say group_exists(group=>"titin"); # 0
# get all groups that user is member of
$res = get_user_groups(user=>"paijo"); # [200, "OK", ["paijo", "satpam"]]
# check whether user is member of a group
$res = is_member(user=>"paijo", group=>"satpam"); # 1
# adding user/group, by default adding user will also add a group with the same
# name
$res = add_user (user =>"ujang", ...); # [200, "OK", {uid=>540, gid=>541}]
$res = add_group(group=>"ujang", ...); # [412, "Group already exists"]
# modify user/group
$res = modify_user(user=>"ujang", home=>"/newhome/ujang"); # [200, "OK"]
$res = modify_group(group=>"titin"); # [404, "Not found"]
# deleting user will also delete user's group
$res = delete_user(user=>"titin");
# change user password
$res = set_user_password(user=>"ujang", pass=>"foobar");
$res = modify_user(user=>"ujang", pass=>"foobar"); # same thing
# add/delete user to/from group
$res = add_user_to_group(user=>"ujang", group=>"wheel");
$res = delete_user_from_group(user=>"ujang", group=>"wheel");
# others
$res = get_max_uid(); # [200, "OK", 65535]
$res = get_max_gid(); # [200, "OK", 65534]
DESCRIPTION
This module can be used to read and manipulate entries in Unix system
password files (/etc/passwd, /etc/group, /etc/group, /etc/gshadow; but
can also be told to search in custom location, for testing purposes).
This module uses a procedural (non-OO) interface. Each function in this
module open and read the passwd files once. Read-only functions like
`list_users()` and `get_max_gid()` open in read-only mode. Functions
that might write to the files like `add_user()` or `delete_group()`
first lock `passwd` file, open in read+write mode and also read the
files in the first pass, then seek to the beginning and write back the
files.
No caching is done so you should do your own if you need to.
FUNCTIONS
add_delete_user_groups
Usage:
add_delete_user_groups(%args) -> [status, msg, result, meta]
Add or delete user from one or several groups.
This can be used to reduce several "add_user_to_group()" and/or
"delete_user_from_group()" calls to a single call. So:
add_delete_user_groups(user=>'u',add_to=>['a','b'],delete_from=>['c','d']);
is equivalent to:
add_user_to_group (user=>'u', group=>'a');
add_user_to_group (user=>'u', group=>'b');
delete_user_from_group(user=>'u', group=>'c');
delete_user_from_group(user=>'u', group=>'d');
except that "add_delete_user_groups()" does it in one pass.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* add_to => *array[str]* (default: [])
List of group names to add the user as member of.
* delete_from => *array[str]* (default: [])
List of group names to remove the user as member of.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
add_group
Usage:
add_group(%args) -> [status, msg, result, meta]
Add a new group.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* gid => *int*
Pick a specific new GID.
Adding a new group with duplicate GID is allowed.
* group* => *str*
* max_gid => *int* (default: 65535)
Pick a range for new GID.
If a free GID between "min_gid" and "max_gid" is not found, error
412 is returned.
* members => *any*
Fill initial members.
* min_gid => *int* (default: 1000)
Pick a range for new GID.
If a free GID between "min_gid" and "max_gid" is not found, error
412 is returned.
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
add_user
Usage:
add_user(%args) -> [status, msg, result, meta]
Add a new user.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* encpass => *str*
Encrypted password.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* expire_date => *int*
The date of expiration of the account, expressed as the number of
days since Jan 1, 1970.
* gecos => *str*
Usually, it contains the full username.
* gid => *int*
Pick a specific GID when creating group.
Duplicate GID is allowed.
* group => *str*
Select primary group (default is group with same name as user).
Normally, a user's primary group with group with the same name as
user, which will be created if does not already exist. You can pick
another group here, which must already exist (and in this case, the
group with the same name as user will not be created).
* home => *str*
User's home directory.
* last_pwchange => *int*
The date of the last password change, expressed as the number of
days since Jan 1, 1970.
* max_gid => *int*
Pick a range for GID when creating group.
* max_pass_age => *int*
The number of days after which the user will have to change her
password.
* max_uid => *int* (default: 65535)
Pick a range for new UID.
If a free UID between "min_uid" and "max_uid" is not found, error
412 is returned.
* min_gid => *int*
Pick a range for GID when creating group.
* min_pass_age => *int*
The number of days the user will have to wait before she will be
allowed to change her password again.
* min_uid => *int* (default: 1000)
Pick a range for new UID.
If a free UID between "min_uid" and "max_uid" is not found, error
412 is returned.
* pass => *str*
Password, generally should be "x" which means password is encrypted
in shadow.
* pass_inactive_period => *int*
The number of days after a password has expired (see max_pass_age)
during which the password should still be accepted (and user should
update her password during the next login).
* pass_warn_period => *int*
The number of days before a password is going to expire (see
max_pass_age) during which the user should be warned.
* shell => *str*
User's shell.
* uid => *int*
Pick a specific new UID.
Adding a new user with duplicate UID is allowed.
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
add_user_to_group
Usage:
add_user_to_group(%args) -> [status, msg, result, meta]
Add user to a group.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* group* => *str*
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
delete_group
Usage:
delete_group(%args) -> [status, msg, result, meta]
Delete a group.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* group* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
delete_user
Usage:
delete_user(%args) -> [status, msg, result, meta]
Delete a user.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
delete_user_from_group
Usage:
delete_user_from_group(%args) -> [status, msg, result, meta]
Delete user from a group.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* group* => *str*
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
get_group
Usage:
get_group(%args) -> [status, msg, result, meta]
Get group details by group name or gid.
Either "group" OR "gid" must be specified.
The function is not dissimilar to Unix's "getgrnam()" or "getgrgid()".
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* gid => *int*
* group => *str*
* with_field_names => *bool* (default: 1)
If false, don't return hash.
By default, a hashref is returned containing field names and its
values, e.g. "{group=>"titin", pass=>"x", gid=>500, ...}". With
"with_field_names=>0", an arrayref is returned instead: "["titin",
"x", 500, ...]".
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
get_max_gid
Usage:
get_max_gid(%args) -> [status, msg, result, meta]
Get maximum GID used.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
get_max_uid
Usage:
get_max_uid(%args) -> [status, msg, result, meta]
Get maximum UID used.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
get_user
Usage:
get_user(%args) -> [status, msg, result, meta]
Get user details by username or uid.
Either "user" OR "uid" must be specified.
The function is not dissimilar to Unix's "getpwnam()" or "getpwuid()".
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* uid => *int*
* user => *str*
* with_field_names => *bool* (default: 1)
If false, don't return hash.
By default, a hashref is returned containing field names and its
values, e.g. "{user=>"titin", pass=>"x", uid=>500, ...}". With
"with_field_names=>0", an arrayref is returned instead: "["titin",
"x", 500, ...]".
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
get_user_groups
Usage:
get_user_groups(%args) -> [status, msg, result, meta]
Return groups which the user belongs to.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* detail => *bool* (default: 0)
If true, return all fields instead of just group names.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* user* => *str*
* with_field_names => *bool* (default: 1)
If false, don't return hash for each entry.
By default, when "detail=>1", a hashref is returned for each entry
containing field names and its values, e.g. "{group=>"titin",
pass=>"x", gid=>500, ...}". With "with_field_names=>0", an arrayref
is returned instead: "["titin", "x", 500, ...]".
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
group_exists
Usage:
group_exists(%args) -> bool
Check whether group exists.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* gid => *int*
* group => *str*
Return value: (bool)
is_member
Usage:
is_member(%args) -> bool
Check whether user is member of a group.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* group* => *str*
* user* => *str*
Return value: (bool)
list_groups
Usage:
list_groups(%args) -> [status, msg, result, meta]
List Unix groups in group file.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* detail => *bool* (default: 0)
If true, return all fields instead of just group names.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* with_field_names => *bool* (default: 1)
If false, don't return hash for each entry.
By default, when "detail=>1", a hashref is returned for each entry
containing field names and its values, e.g. "{group=>"titin",
pass=>"x", gid=>500, ...}". With "with_field_names=>0", an arrayref
is returned instead: "["titin", "x", 500, ...]".
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
list_users
Usage:
list_users(%args) -> [status, msg, result, meta]
List Unix users in passwd file.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* detail => *bool* (default: 0)
If true, return all fields instead of just usernames.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* with_field_names => *bool* (default: 1)
If false, don't return hash for each entry.
By default, when "detail=>1", a hashref is returned for each entry
containing field names and its values, e.g. "{user=>"titin",
pass=>"x", uid=>500, ...}". With "with_field_names=>0", an arrayref
is returned instead: "["titin", "x", 500, ...]".
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
list_users_and_groups
Usage:
list_users_and_groups(%args) -> [status, msg, result, meta]
List Unix users and groups in passwd/group files.
This is basically "list_users()" and "list_groups()" combined, so you
can get both data in a single call. Data is returned in an array. Users
list is in the first element, groups list in the second.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* detail => *bool* (default: 0)
If true, return all fields instead of just names.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* with_field_names => *bool* (default: 1)
If false, don't return hash for each entry.
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
modify_group
Usage:
modify_group(%args) -> [status, msg, result, meta]
Modify an existing group.
Specify arguments to modify corresponding fields. Unspecified fields
will not be modified.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* admins => *str*
It must be a comma-separated list of user names, or empty.
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* encpass => *str*
Encrypted password.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* gid => *int*
Numeric group ID.
* group* => *str*
Group name.
* members => *str*
List of usernames that are members of this group, separated by
commas.
* pass => *str*
Password, generally should be "x" which means password is encrypted
in gshadow.
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
modify_user
Usage:
modify_user(%args) -> [status, msg, result, meta]
Modify an existing user.
Specify arguments to modify corresponding fields. Unspecified fields
will not be modified.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* encpass => *str*
Encrypted password.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* expire_date => *int*
The date of expiration of the account, expressed as the number of
days since Jan 1, 1970.
* gecos => *str*
Usually, it contains the full username.
* gid => *int*
Numeric primary group ID for this user.
* home => *str*
User's home directory.
* last_pwchange => *int*
The date of the last password change, expressed as the number of
days since Jan 1, 1970.
* max_pass_age => *int*
The number of days after which the user will have to change her
password.
* min_pass_age => *int*
The number of days the user will have to wait before she will be
allowed to change her password again.
* pass_inactive_period => *int*
The number of days after a password has expired (see max_pass_age)
during which the password should still be accepted (and user should
update her password during the next login).
* pass_warn_period => *int*
The number of days before a password is going to expire (see
max_pass_age) during which the user should be warned.
* shell => *str*
User's shell.
* uid => *int*
Numeric user ID.
* user* => *str*
User (login) name.
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
set_user_groups
Usage:
set_user_groups(%args) -> [status, msg, result, meta]
Set the groups that a user is member of.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* groups* => *array[str]* (default: [])
List of group names that user is member of.
Aside from this list, user will not belong to any other group.
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
set_user_password
Usage:
set_user_password(%args) -> [status, msg, result, meta]
Set user's password.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* backup => *bool* (default: 0)
Whether to backup when modifying files.
Backup is written with ".bak" extension in the same directory.
Unmodified file will not be backed up. Previous backup will be
overwritten.
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* pass* => *str*
* user* => *str*
Returns an enveloped result (an array).
First element (status) is an integer containing HTTP status code (200
means OK, 4xx caller error, 5xx function error). Second element (msg) is
a string containing error message, or 'OK' if status is 200. Third
element (result) is optional, the actual result. Fourth element (meta)
is called result metadata and is optional, a hash that contains extra
information.
Return value: (any)
user_exists
Usage:
user_exists(%args) -> bool
Check whether user exists.
This function is not exported by default, but exportable.
Arguments ('*' denotes required arguments):
* etc_dir => *str* (default: "/etc")
Specify location of passwd files.
* uid => *int*
* user => *str*
Return value: (bool)
HOMEPAGE
Please visit the project's homepage at
<https://metacpan.org/release/Unix-Passwd-File>.
SOURCE
Source repository is at
<https://github.com/perlancar/perl-Unix-Passwd-File>.
BUGS
Please report any bugs or feature requests on the bugtracker website
<https://rt.cpan.org/Public/Dist/Display.html?Name=Unix-Passwd-File>
When submitting a bug or request, please include a test-file or a patch
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SEE ALSO
Old modules on CPAN which do not support shadow files are pretty useless
to me (e.g. Unix::ConfigFile). Shadow passwords have been around since
1988 (and in Linux since 1992), FFS!
Passwd::Unix. I created a fork of Passwd::Unix v0.52 called
Passwd::Unix::Alt in 2011 to fix some of the deficiencies/quirks in
Passwd::Unix, including: lack of tests, insistence of running as root
(despite allowing custom passwd files), use of not-so-ubiquitous bzip2,
etc. Then in 2012 I decided to create Unix::Passwd::File. Here are how
Unix::Passwd::File differs compared to Passwd::Unix (and
Passwd::Unix::Alt):
* tests in distribution
* no need to run as root
* no need to be able to read the shadow file for some operations
For example, "list_users()" will simply not return the "encpass"
field if the shadow file is unreadable. Of course, access to shadow
file is required when getting or setting password.
* strictly procedural (non-OO) interface
I consider this a feature :-)
* detailed error message for each operation
* removal of global error variable
* working locking
Locking is done by locking "passwd" file.
Setup::Unix::User and Setup::Unix::Group, which use this module.
Rinci
AUTHOR
perlancar <perlancar@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2017, 2016, 2015, 2014, 2012 by
perlancar@cpan.org.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.